Page 1 of 2 Office of Ground Water and Drinking Water

November 4, 2013

MEMORANDUM

SUBJECT: Basis for Expedited Approval of Hach Company Method 10260: Determination of Chlorinated Oxidants (Free and Total) in Water using Disposable Planar Reagent-Filled Cuvettes and Mesofluidic Channel Colorimetry

FROM: Glynda Smith, Chemist, SRMD/TSC Steve Wendelken, Chemist, SRMD/TSC

TO: The Record

Hach Company’s disposable Planar Reagent-Filled Cuvette (PRFC) method measures free, total and combined chlorine as an optional alternate test procedure to Standard Method 4500-Cl G which is approved in the national primary drinking water regulations at 40 CFR 141.74(a)(2) for determination of free and total chlorine, and at 40 CFR 141.131(c)(1) for determination of free, total, and combined
chlorine.

An automated instrument draws a water sample into a cuvette that is prefilled with the reagents that are required to perform DPD (N,N-diethyl-p-phenylenediamine) colorimetric chlorine tests. Automation of the DPD determination relative to the manual procedure described in the approved method reduces errors associated with reagent addition, mixing and color development.

Three laboratories participated in a multi-laboratory validation study. The laboratories evaluated precision and accuracy in a variety of drinking water matrices (e.g., low ionic strength, high ionic strength, and tap water samples drawn from both surface water and ground water sources). MDLs were determined for free chlorine and for total chlorine. Accuracy and precision were evaluated in all test matrices by fortifying replicates at 2.0 mg Cl 2 /L. The Hach PRFC method was evaluated side by side with the approved method, Standard Method 4500-Cl G, which employs DPD solid reagents. The complete data summary is provided in the Hach ATP Validation Report. Briefly, the results are as follows:

Free Chlorine

 The PRFC method the approved manual DPD method yielded the same MDLs (0.019 mg/L) in low ionic strength water. In high ionic strength water, the PRFC method yielded a pooled MDL of 0.025 mg/L and the approved DPD method a pooled MDL of 0.020 mg/L.

 The pooled average recovery in low ionic strength water fortified at 2 mg/L free chlorine was 103% for the results obtained with the PRFC method relative to the approved manual DPD method and 102% in high ionic strength water fortified at 2 mg/L free chlorine.

 The pooled average recovery for all matrices fortified at 2 mg/L free chlorine was 103.9% for the PRFC method relative to the approved manual DPD method (based on 120 tap water samples drawn from ground water and surface water sources covering a pH range of 6.0 to 8.8).

 The interference in the free chlorine determination from a 2.0 mg/L monochloramine standard was determined to be 6.3% in the PRFC method and 4.0% with the approved manual DPD
method.Page 2 of 2

Total Chlorine

 In low ionic strength water, the PRFC method yielded a pooled MDL of 0.025 mg/L compared to the approved manual DPD method which had a pooled MDL of 0.050 mg/L. In high ionic strength water, the pooled MDL for the PRFC method was 0.033 mg/L and the approved manual DPD method was 0.040 mg/L.

 The pooled average recovery in low ionic strength water fortified at 2 mg/L total chlorine was

9 3 % for the results obtained with the PRFC method relative to the approved manual DPD
method and 9 2 % in high ionic strength water fortified at 2 mg/L total chlorine

.

 The pooled average recovery for all matrices fortified at 2 mg/L total chlorine was 96.5% for the
PRFC method relative to the approved manual DPD method (based on 114 tap water samples drawn from ground water and surface water sources covering a pH range of 6.0 to 8.8).

Based on evaluation of the accuracy, precision and sensitivity determined in the multi

- laboratory
vali dation study

, the Hach PRFC method is equally as effective as Standard Method 4500

- Cl G in determining free, combined, and total chlorine in drinking water.